pg.ddx.io pgsql-docs@postgresql.org mailing list archive
help / color / mirror / Atom feed4.2.7. Aggregate Expressions
4+ messages / 3 participants
[nested] [flat]
Commits from this thread:
2026-10-10 0a38a8ff3f doc: add SQL query showing handling of NULLs by aggregates
* 4.2.7. Aggregate Expressions
@ 2026-08-27 14:26 PG Doc comments form <noreply@postgresql.org>
0 siblings, 1 reply; 4+ messages in thread
From: PG Doc comments form @ 2026-08-27 14:26 UTC (permalink / raw)
To: pgsql-docs@lists.postgresql.org; +Cc: y.saburov@gmail.com
The following documentation comment has been logged on the website:
Page: https://www.postgresql.org/docs/18/sql-expressions.html
Description:
Can you add a code block with an example?
Perhaps something like this:
```psql
db=# WITH vals (f1) AS ( VALUES (1),(3),(4),(3),(2),(null) )
SELECT count(*), count(f1), COUNT(DISTINCT f1) FROM vals;
count | count | count
-------+-------+-------
6 | 5 | 4
(1 row)
```
After:
>> For example, count(*) returns the total number of input rows; count(f1)
returns the number of input rows in which f1 is not null, since count
ignores null values; and count(distinct f1) returns the number of distinct
non-null values of f1.
We haven’t seen the term “f1” before—and the paragraph doesn’t specify that
this is a field.
^ permalink raw reply [nested|flat] 4+ messages in thread
* Re: 4.2.7. Aggregate Expressions
@ 2026-09-15 21:28 Bruce Momjian <bruce@momjian.us>
parent: PG Doc comments form <noreply@postgresql.org>
0 siblings, 1 reply; 4+ messages in thread
From: Bruce Momjian @ 2026-09-15 21:28 UTC (permalink / raw)
To: y.saburov@gmail.com; pgsql-docs@lists.postgresql.org
On Thu, Aug 27, 2026 at 02:26:46PM +0000, PG Doc comments form wrote:
> The following documentation comment has been logged on the website:
>
> Page: https://www.postgresql.org/docs/18/sql-expressions.html
> Description:
>
> Can you add a code block with an example?
>
> Perhaps something like this:
>
> ```psql
> db=# WITH vals (f1) AS ( VALUES (1),(3),(4),(3),(2),(null) )
> SELECT count(*), count(f1), COUNT(DISTINCT f1) FROM vals;
>
> count | count | count
> -------+-------+-------
> 6 | 5 | 4
> (1 row)
> ```
>
> After:
>
> >> For example, count(*) returns the total number of input rows; count(f1)
> returns the number of input rows in which f1 is not null, since count
> ignores null values; and count(distinct f1) returns the number of distinct
> non-null values of f1.
I see your point that this could be clearer. How is this patch?
--
Bruce Momjian <bruce@momjian.us> https://momjian.us
EDB https://enterprisedb.com
Do not let urgent matters crowd out time for investment in the future.
Attachments:
agg_null.diff (text/x-diff, 1.2K) download
diff --git a/doc/src/sgml/syntax.sgml b/doc/src/sgml/syntax.sgml
index 67482996861..a697218c8b3 100644
--- a/doc/src/sgml/syntax.sgml
+++ b/doc/src/sgml/syntax.sgml
@@ -1602,11 +1602,19 @@ sqrt(2)
</para>
<para>
- For example, <literal>count(*)</literal> yields the total number
- of input rows; <literal>count(f1)</literal> yields the number of
- input rows in which <literal>f1</literal> is non-null, since
- <function>count</function> ignores nulls; and
- <literal>count(distinct f1)</literal> yields the number of
+ For example, in this query:
+<programlisting>
+WITH vals (f1) AS ( VALUES (1),(3),(4),(3),(2),(null) )
+SELECT count(*) AS total, count(f1) AS non_null, COUNT(DISTINCT f1) AS distinct
+FROM vals;
+ total | non_null | distinct
+-------+----------+----------
+ 6 | 5 | 4
+</programlisting>
+ <literal>total</literal> yields the total number of input rows;
+ <literal>non_null</literal> yields the number of input rows in which
+ <literal>f1</literal> is non-null, since <function>count</function>
+ ignores nulls; and <literal>distinct</literal> yields the number of
distinct non-null values of <literal>f1</literal>.
</para>
* Re: 4.2.7. Aggregate Expressions
@ 2026-09-16 05:20 Laurenz Albe <laurenz.albe@cybertec.at>
parent: Bruce Momjian <bruce@momjian.us>
0 siblings, 1 reply; 4+ messages in thread
From: Laurenz Albe @ 2026-09-16 05:20 UTC (permalink / raw)
To: Bruce Momjian <bruce@momjian.us>; y.saburov@gmail.com; pgsql-docs@lists.postgresql.org
On Tue, 2026-09-15 at 17:28 -0400, Bruce Momjian wrote:
> I see your point that this could be clearer. How is this patch?
I think that is a good example.
+1 for that change.
Yours,
Laurenz Albe
^ permalink raw reply [nested|flat] 4+ messages in thread
* Re: 4.2.7. Aggregate Expressions
@ 2026-10-10 02:14 Bruce Momjian <bruce@momjian.us>
parent: Laurenz Albe <laurenz.albe@cybertec.at>
0 siblings, 0 replies; 4+ messages in thread
From: Bruce Momjian @ 2026-10-10 02:14 UTC (permalink / raw)
To: Laurenz Albe <laurenz.albe@cybertec.at>; +Cc: y.saburov@gmail.com; pgsql-docs@lists.postgresql.org
On Wed, Sep 16, 2026 at 07:20:56AM +0200, Laurenz Albe wrote:
> On Tue, 2026-09-15 at 17:28 -0400, Bruce Momjian wrote:
> > I see your point that this could be clearer. How is this patch?
>
> I think that is a good example.
> +1 for that change.
Great, patch applied back to PG 19.
--
Bruce Momjian <bruce@momjian.us> https://momjian.us
EDB https://enterprisedb.com
Do not let urgent matters crowd out time for investment in the future.
^ permalink raw reply [nested|flat] 4+ messages in thread
end of thread, other threads:[~2026-10-10 02:14 UTC | newest]
Thread overview: 4+ messages (download: mbox mbox.gz follow: Atom feed)
-- links below jump to the message on this page --
2026-08-27 14:26 4.2.7. Aggregate Expressions PG Doc comments form <noreply@postgresql.org>
2026-09-15 21:28 ` Bruce Momjian <bruce@momjian.us>
2026-09-16 05:20 ` Laurenz Albe <laurenz.albe@cybertec.at>
2026-10-10 02:14 ` Bruce Momjian <bruce@momjian.us>
This inbox is served by DDX for PostgreSQL; see mirroring instructions
for how to clone and mirror all data and code used for this inbox